Thousands of women a year are giving birth after admitting having drunk too much during their pregnancies, a Sky News investigation has found.

Although government guidelines warn pregnant women against drinking more than four units a week - equivalent to two large glasses of wine - hospitals have recorded a significant number drinking much more.

The first hospital figures of their kind suggest that more than 2,000 babies a year are born to mothers who have breached alcohol guidelines.

Image Caption:Heavy drinking during pregnancy increases the health risks to children

And experts say the problem is likely to be much worse as NHS trusts rely on women to honestly report how much they have drunk.

The figures - obtained by Sky News following a Freedom of Information request - show that in the last three years, 2,496 mothers-to-be told hospital staff in England they were drinking at least four units of alcohol a week.

Video:Call For Drink Ban On Pregnant Mums

In the worst cases, South Tees Hospital NHS Foundation Trust recorded four women drinking more than 34 units a week over that period.

Liverpool Women's hospital recorded 17 women drinking more than 20 units a week, and two drinking more than 10 units every day.

However, fewer than half of all England NHS trusts (45 out of 108) were able to supply figures.

Extrapolating the figures suggests that just over 2,000 mothers-to-be admit to drinking too much during pregnancy.

Overall, the hospital statistics showed around 0.5% of pregnant women admitted drinking more than the Department of Health guidelines.

Heavy drinking during pregnancy increases the risk that babies will be born with foetal alcohol syndrome - a life-long condition that can leave children physically and mentally disabled.

Video:Pregnancy Drinking Lowers Baby IQ

One woman whose son was born with foetal alcohol syndrome after she drunk heavily during pregnancy following years of alcoholism, said little was done to help her break her addiction.

"When I was five months pregnant, I told the midwife that I was an alcoholic and that I couldn't control my drinking," said Samantha Marchant, 40, from Slough.

"They referred me to a drug and alcohol team which put me on a drinks diary ... I'd have liked them to say 'you can have a place in rehab', but it wasn't offered."

"I didn't know about the biology of what happens if you drink in pregnancy," added Ms Marchant, who is now a recovered alcoholic and works to raise other women's awareness of the dangers of drinking during pregnancy.

Dr Raja Mukherjee, lead clinician for the national foetal alcohol spectrum disorder clinic at Surrey and Borders Partnership NHS Foundation Trust, said: "All the research has shown that high level alcohol exposure causes significant damage to a developing foetus.

"We know that women are drinking more .. 90% of women in this country drink and they don't all suddenly stop when they are pregnant."

The figures obtained by Sky also reveal significant gaps in the monitoring of alcohol consumption during pregnancy.

More than 90% of hospitals do not ask women about their alcohol consumption throughout pregnancy, and three of the NHS trusts did not ask pregnant women about their drinking at all.